Although so-called radiography employing silver halide photography is conventionally used to obtain radiographic images, there also has been developed a radiographic imaging method not using silver halide photographic material. Thus, an imaging method is disclosed, in which radiation that has been transmitted through an object is absorbed by phosphor, followed by exciting the phosphor with an energy to cause a radiation energy accumulated in the phosphor to radiate in the form of fluorescence, and imaging is achieved by detecting the fluorescence.
Specifically, U.S. Pat. No. 3,859,527 discloses a radiation image conversion method, in which a panel comprising on a support a photostimulable phosphor layer is employed using either or both visible light and infrared rays as the stimulating energy.
There have been developed radiation image conversion methods using a photostimulable phosphor (hereinafter, also denoted simply as a stimulable phosphor) exhibiting enhanced luminance and high sensitivity, including, for example, a radiation image conversion method employing BaFX:Eu2+type phosphor (X: Cl, Br, I), as described in Japanese Patent Publication Open to Public Inspection No. 59-75200 (hereinafter, referred to as Japanese Patent O.P.I. Publication); a radiation image conversion method employing an alkali halide phosphor, as described in Japanese Patent O.P.I. Publication No. 61-72087; a radiation image conversion method employing an alkali halide phosphor containing, as coactivators, Tl+ and metals such as Ce3+, Sm3+, Eu3+, Y3+, Ag+, Mg2+, Pb2+ or In3+, as described in Japanese Patent O.P.I. Publication Nos. 61-73786 and 61-73787.
Recently, a radiation image conversion panel exhibiting further enhanced sharpness has been desired in the field of diagnostic image analysis. Of these, an attempt in controlling the form of stimulable phosphor grains to enhance sensitivity and sharpness was made as a means for improving sharpness of radiographic images.
For example, Japanese Patent O.P.I. Publication No. 61-142497 discloses a method of using a stimulable phosphor layer comprising a fine pseudo-columnar block which has been formed by accumulating a stimulable phosphor on a support having fine protruded patterns.
Further, proposed methods include a method to use a radiation image conversion panel having a stimulable phosphor layer, in which, as described in Japanese Patent O.P.I. Publication No. 61-142500, cracks between columnar blocks, which are prepared by accumulating a stimulable phosphor on a support having a fine pattern, are subjected to a shock treatment so that the aforesaid cracks are allowed to grow. Further, Japanese Patent O.P.I. Publication 62-39737 discloses a method of using a radiation image conversion panel having a stimulable phosphor layer with a pseudo-columnar form which has been formed by producing cracks on the layer surface side. Japanese Patent O.P.I. Publication 62-110200 proposes a method in which a stimulable phosphor layer having voids is formed by vapor deposition onto the upper surface of a support, followed by growing voids by subjecting a heating treatment to produce cracks.
Japanese Patent O.P.I. Publication No. 2-58000 proposed a radiation image conversion panel having a stimulable phosphor layer, in which long and thin columnar crystals were formed with an incline at a given angle toward the direction normal to the support.
Recently, a radiation image conversion panel using a stimulable phosphor containing an alkali halide such as CsBr as a basic substance and Eu as an activator, and the use of activator Eu leading to enhanced X-ray conversion efficiency, which has formerly not been achieved.
While the image quality is further improved in such a way, and the radiation image conversion panel is increasingly used for photography, a radiation image conversion panel exhibiting higher X-ray irradiation resistance property is preferred since it is well known that luminance of the radiation image conversion panel via X-ray irradiation is degraded.